The present invention generally relates to a silver recovery device and more particularly to an apparatus which removes silver from photographic developing fluids such as fixers and developers.
Photographic films including photographic paper typically comprise a base material coated with a light-sensitive emulsion. The emulsion normally contains various silver salts, such as silver halides. During the developing process, the films are placed in various solutions that chemically react with the emulsion layer in order to develop an image. During this process, some of the silver salts and silver halides become dissolved or suspended within the developing solutions. For instance, one type of film developing solution, called a fixer, is specifically used to dissolve out any silver halides that were not exposed when the picture or image was taken.
Once these solutions become spent, it is desirable to recover the silver prior to disposing the solutions for two important reasons. First, the silver that can be recovered from photographic developing solutions is very valuable. Silver, which is considered a precious metal, has many uses and applications while being very expensive to obtain. Even recovering small amounts of silver in developing solutions can be economically advantageous.
The second reason to remove silver from photographic solutions, and perhaps more importantly, is that the silver containing solutions are considered pollutants. In fact, in many areas the silver concentration of the solution must be below five parts per million before the solution is considered safe for disposal. As such, recovering the silver from photographic developing solutions is environmentally necessary.
In the past, others have attempted to develop various devices for recovering silver from spent, photographic processing fluids. For instance, one prior art construction discloses a canister for the recovery of silver from silver-containing waste fluids. The canister includes an inner and an outer element, each removable from the other. The inner element has a vented necked top matable to a bottom container. The bottom container includes at least one foot and has a plurality of holes located on the bottom to permit fluid to rise from the bottom to the vented necked top. Fluid enters the canister, flows to the bottom, rises within the inner element and then exits out an exit mating means connected to the necked top. The inner element contains a silver recovery media such as steel wool in addition to small amounts of copper or cadmium salt. When the waste solution enters the canister, a chemical replacement reaction occurs between the silver contained in the solution and the iron contained within the steel wool.
The present inventor is also the listed inventor in U.S. Pat. No. 5,472,176 entitled "Silver Recovery Device," which is incorporated herewith in its entirety by reference thereto. In that application, a silver recovery device is disclosed in which, in one embodiment, a silver recovery element is forceably loaded into a tubular liner, causing the liner to apply a compressive force to the recovery element. The compressive force was found to prevent the formation of channels within the silver recovery element during the processing of fluids and also to cause fluid to filter more slowly through the device. The invention or inventions disclosed in the inventor's prior application made great advances in the state of the art.
The present invention is directed to further improvements in silver recovery devices. Specifically, difficulties have been encountered when processing solutions used in developing color photography. In particular, photographic solutions used to develop color films typically contain buoyant particulate matter. The particulate matter tends to float within the silver recovery device, sometimes exiting through the fluid outlet channel. Over time, the particulate matter can agglomerate within the device or in the outlet channel causing blockage of fluid flow. When blockage occurs, the fluid being processed will either be prevented from entering the silver recovery device or will overflow and bypass the silver exchange media.
In view of the above, one aspect of the present invention is to overcome problems associated with processing color film photographic fluids. In particular, the device of the present invention may include a filter element for preventing any particulate matter contained within the photographic fluid from exiting the device. Also, in another embodiment, the present invention is constructed so that pressure may be applied to the entering fluids, preventing the formation of clogs or blockages within the device or downstream. Many other advantages and features of the present invention will be apparent from the following description.